PSI - Issue 3

F. Berto et al. / Procedia Structural Integrity 3 (2017) 162–167 F. Berto et al. / Structural Integrity Procedia 00 (2017) 000–000

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Fig. 3. 40CrMoV13.9 fatigue data, hour-glass shaped specimens.

In the high cycle fatigue regime the critical SED range for un-notched specimens can be simply evaluated by using the following expression:

2 / 2

c W    

E

At 2×10 6 cycles, by using the mean value of the stress range from plain specimens (241 MPa), the SED range is 0.22 MJ/m 3 . In parallel, the averaged SED for plates with central holes have been calculated by means of Ansys code modelling one quarter of the plate and taking advantages of the double symmetry. The radius of the control volume has been varied to match the SED value previously determined from the un-notched specimens at 2×10 6 cycles. The material has been assumed isotropic and linear elastic with the Young’s modulus E = 133000 MPa (which is typical of CuBe alloy under investigation) and the Poisson’s ratio ν = 0.3. The 8-nodes iso-parametric element plane 82, with plane strain key-option has been selected. a

b

Fig. 4 (a) synthesis of Cu-Be fatigue data by means of local SED; (b) critical volume of plate with central hole.

The simulation has been repeated for different values of R c , ranging from 0.2 to 0.9 mm (with a step of 0.1 mm). Coarse meshes have been used because the SED value is independent of the mesh pattern as documented in Lazzarin et al. (2010; 2008). For the plates with the central hole, the lower deviation with respect to the reference values (0.22 MJ/m 3 ) has been obtained considering a control radius R c = 0.6 mm. For this value, in fact, the SED range has been found to be 0.24 MJ/m 3 , which is very close to that of un-notched specimens. The fatigue data are plotted in terms of